fix(txnames): Prevent recursion error (#59421)

Prevent recursion errors in transaction clustering. This only happens
for very deep trees, which do not make good transaction names or span
descriptions in the first place.

Fixes [SENTRY-170T](https://sentry.sentry.io/issues/4559413640/)

Author: jjbayer

src/sentry/ingest/transaction_clusterer/tree.py

@@ -68,6 +68,10 @@ class Merged:
 #: Separator by which we build the tree
 SEP = "/"
 
+#: Maximum tree depth. URLs with more than 200 segments do not seem useful,
+#: and we occasionally run into `RecursionError`s.
+MAX_DEPTH = 200
+
 
 logger = logging.getLogger(__name__)
 
@@ -80,7 +84,7 @@ def __init__(self, *, merge_threshold: int) -> None:
 
     def add_input(self, strings: Iterable[str]) -> None:
         for string in strings:
-            parts = string.split(SEP)
+            parts = string.split(SEP, maxsplit=MAX_DEPTH)
             node = self._tree
             for part in parts:
                 node = node.setdefault(part, Node())

tests/sentry/ingest/test_transaction_clusterer.py

@@ -63,6 +63,17 @@ def test_single_leaf():
     assert clusterer.get_rules() == ["/a/*/**"]
 
 
+def test_deep_tree():
+    clusterer = TreeClusterer(merge_threshold=1)
+    transaction_names = [
+        1001 * "/.",
+    ]
+    clusterer.add_input(transaction_names)
+
+    # Does not throw an exception:
+    clusterer.get_rules()
+
+
 @mock.patch("sentry.ingest.transaction_clusterer.datasource.redis.MAX_SET_SIZE", 5)
 def test_collection():
     org = Organization(pk=666)